1 files changed, 90 insertions, 0 deletions
diff --git a/Sources/NorgKeyboardToolbar/EditorSnippet.swift b/Sources/NorgKeyboardToolbar/EditorSnippet.swift
new file mode 100644
index 0000000..b87d2b1
--- /dev/null
+++ b/Sources/NorgKeyboardToolbar/EditorSnippet.swift
@@ -0,0 +1,90 @@
+import Foundation
+
+/// The available editor snippets to show in the toolbar.
+enum EditorSnippet: String, CaseIterable, Identifiable, Sendable {
+  case heading
+  case task
+  case weakReverse
+  case strongReverse
+  case code
+
+  public var id: String { rawValue }
+
+  /// The text inserted, with the cursor offset (in characters).
+  public var template: (text: String, cursor: Int) {
+    switch self {
+    case .heading: return ("* ", 2)
+    case .task: return ("- ( ) ", 6)
+    case .weakReverse: return ("---", 3)
+    case .strongReverse: return ("===", 3)
+    case .code: return ("@code\n\t\n@end", 7)
+    }
+  }
+
+  /// Applies the snippet, returning the updated text and new cursor offset.
+  public func apply(to text: String, cursor: Int) -> (text: String, cursor: Int) {
+    let characters = Array(text)
+    let position = min(max(cursor, 0), characters.count)
+
+    switch self {
+    case .heading where isInBareMarker(characters, at: position, markers: ["*"]):
+      return promoteHeading(characters, at: position)
+    case .task where isInBareMarker(characters, at: position, markers: ["*", "~"]):
+      return addTask(toMarker: characters, at: position)
+    default:
+      return insertOnNewLine(in: characters, cursor: position)
+    }
+  }
+
+  // MARK: - Marker-aware behaviours
+
+  /// Whether the is at a position with only `markers` and spaces, and contains
+  /// at least one marker.
+  private func isInBareMarker(_ characters: [Character], at position: Int, markers: Set<Character>)
+    -> Bool {
+    let lineStart = LineScanner.lineStart(in: characters, at: position)
+    let prefix = characters[lineStart..<position]
+    return prefix.contains(where: markers.contains)
+      && prefix.allSatisfy { markers.contains($0) || $0 == " " }
+  }
+
+  /// Adds a `*` after the leading run of spaces and stars on the cursor's line.
+  private func promoteHeading(_ characters: [Character], at position: Int) -> (
+    text: String, cursor: Int
+  ) {
+    let lineStart = LineScanner.lineStart(in: characters, at: position)
+
+    var insertAt = lineStart
+    while insertAt < characters.count, characters[insertAt] == " " { insertAt += 1 }
+    while insertAt < characters.count, characters[insertAt] == "*" { insertAt += 1 }
+
+    var result = characters
+    result.insert("*", at: insertAt)
+    return (String(result), insertAt <= position ? position + 1 : position)
+  }
+
+  /// Inserts a task marker `( ) ` at the cursor, turning a heading or
+  /// ordered-list item into a task.
+  private func addTask(toMarker characters: [Character], at position: Int) -> (
+    text: String, cursor: Int
+  ) {
+    var result = characters
+    result.insert(contentsOf: "( ) ", at: position)
+    return (String(result), position + 4)
+  }
+
+  /// Inserts the snippet's text on a new line beneath the cursor's line.
+  private func insertOnNewLine(in characters: [Character], cursor position: Int) -> (
+    text: String, cursor: Int
+  ) {
+    // An empty document takes the snippet as-is, with no leading newline.
+    guard !characters.isEmpty else { return template }
+
+    let lineEnd = LineScanner.lineEnd(in: characters, at: position)
+
+    let prefix = String(characters[0..<lineEnd])
+    let suffix = String(characters[lineEnd...])
+    let newText = prefix + "\n" + template.text + suffix
+    return (newText, lineEnd + 1 + template.cursor)
+  }
+}